On the status of the genus Pinguicollum (Tetraphyllidea: Onchobothriidae) with a redescription of P. pinguicollum.

Material of the poorly known Pinguicollum pinguicollum from Raja spp. in California from the personal collections of Nathan Riser and Mike Moser was examined by light and scanning electron microscopy. The presence of unusual triloculated bothridia covered with a layer of tissue, but capable of protruding through an aperture in this tissue, was confirmed. The species is also unusual in its lack of a muscular pad and apical sucker on each bothridium and in its possession of bifid hooks in which the axial prongs are conspicuously shorter than the abaxial prongs. The scolex was interpreted to consist of a short bothridial region and an elongate cephalic peduncle containing 4 pairs of robust longitudinal muscle bundles. The segment morphology is described in detail and figured for the first time. The ovary is bilobed in cross section; the testes are arranged in multiple rows in cross section. The apex of the scolex was found to possess elongate, filiform microtriches. The distal surfaces of the protrusible regions of the bothridia were covered with short filiform microtriches in the anterior and both short filiform microtriches and spiniform microtriches on the posterior bothridial surfaces. The remainder of the scolex and cephalic peduncle were covered with densely packed, spiniform microtriches of varying sizes. Based on the unusual bothridia, robust cephalic peduncle, and lack of muscular pad and apical sucker on the bothridia, it is recommended that the genus be considered to be valid. As all attempts to locate the type material of the species failed, a neotype is designated to facilitate future study of the genus.